It's tough, and they change constantly, and one of my favorite the 1911A1 has been named but:

Colt Dragoon - Not really a mil-surp unless (unlike me) you can afford the originals, but I settle for my Italian repros. I love revolvers especially open top Colts, and , not counting the rare and limited production Walker, the hulking Dragoon is the grand-daddy of the modern big-bore magnum revolvers, eliminating some of the weaknesses of the Walkers.It truly was the "magnum" of it's day long before the term magnum even existed. It saw use in the early "Wild West", the Civil War on both sides, the early Indian War campaign and long after cartridges came into common use it still rode in the holsters of a few rough and tumble characters, with examples of cartridge conversion Dragoons from the western era found today. With 50+ gr. of BP pushing a big .454 round ball it packed more punch than the venerable .45 Long Colt or 44-40. Even though it's hopelessly obsolete by today's standards I would feel well armed with my repro, at least for 6 rounds as reloading under fire would be nearly impossible unless I had good cover and 3 minutes of time to spare. When the Dragoon speaks at the range it really draws a crowd, too, with a rolling "pa-TOOM" followed by a cloud of acrid smoke. Love it!

S&W Model 10 .38 Special (and .38 S&W) - not much to say, simple, reliable and elegant in it's ruggedness. From 1899 to today, as both the "M&P" and Model 10, it has been a mainstay. The .38 Special round has served in every capacity from military to police in this revolver, from WWI to Vietnam, to today in limited numbers. You can still find one of the millions of Model 10's produced for $200 and it will likely outlast you.

Any of the 1880's-90's era European smaller caliber service revolvers- Such as the 1895 Nagant, the Swiss 1882, French 1892,1898 Rast-Gasser, etc. Extremely rugged, very finely made with simple, durable actions, the fact that so many are around today in perfect shootable condition after in some cases being through at least two World Wars and suffering all kinds of abuse, speaks volumes. They are only handicapped by wierd calibers (by today's standards) and anemic loadings.French 1892's saw use as late as the 1950's in France's Indochina campaign. I have a Rast Gasser that has been through hell and back somewhere in South America where it was sold privately as surplus, probably after seeing service in WWI to boot. Even with severe neglect and some homemade repairs it functions perfectly and shoots well with .32 H&R mags. This kind of abuse would cripple a Colt or Smith & Wesson without serious gunsmith attention. As much as I love the early American DA's like the 1892 Colt and S&W breaktops, they were no where near as rugged as these revolvers.

Of course the 1911A1, for the reasons already mentioned, timeless, powerful and rugged. Also the Tokarevs, for me mainly because it's a ripoff of the Browning design made simpler and uses the cheapest milsurp ammo around right now. I have a Chinese Tok and I shoot the life out of it, so much that the slide rails are starting to mushroom.

I actually have more fun with this, a Belgian made Norwegian Nagant in 7.5. No less of a masterpiece of gunmaking, from a time when labor and steel was cheap and gunmakers took pride in their military contract firearms, also because competition was fierce and Nagant wanted to turn out the best revolvers in the world so that Norway, Russia and others wouldn't look somewhere else for sidearms. The prices of these revolvers, even in Good condition rivals that of a new S&W but I feel it is worth it, and this Nagant, despite seeing lots of holster time and some firing, is still as tight and functional as it was back in the 1890's-1940's when these were still in use by Norway. It can drop .32 S&W longs or .32 H&R mags into 3" groups at about 15 yards,with minimal case bulging, not bad for using "makeshift" ammo, I'm sure it would do much better with proper 7.5 ammo. I ran about 1,000 rounds through this revolver, not one of which was 7.5 and I love to take it out back and plink with it due to the low noise and low power of the .32 long wadcutters I (used to) get cheap from Fiocchi. Makes a perfect little "out in the pasture" shooter when you want to be courteous to your neighbors.